Magnetically confined graphene quantum dots

• Applicant: Professor Dr. Markus Morgenstern
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: from 2018 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 400112579

• Final Report Year: 2025

Final Report Abstract

Quantum dots in graphene have recently been developed to a level of control such that they are a possible contender for spin, valley or Kramers qubits in solids. This employs bilayer graphene with a tunable band gap. Partially, amazing relaxation times of the binary quantum degree of freedom up to ~40 s are achieved. Moreover, first coherence properties within such quantum dots have been probed. The situation was quite different when this project was granted in 2018. Based on successful measurements using the tip induced quantum dot in monolayer graphene, we proposed to develop the demonstrated magnetic confinement of electrons enabling precise control of spin and valley degrees of freedom towards a scalable platform, but initially including the tip induced quantum dot by employing its lateral control. During the course of the project, we made significant progress in preparation of adequate samples by stacking methods optimized for scanning tunneling spectroscopy and mask technology for in-situ preparation of contacts, but refrained from optimizing the magnetically confined quantum dots, since not being competitive anymore with the meanwhile established bilayer graphene quantum dots due to the required high magnetic fields. Instead, we have used the gained knowledge for refined strategies to avoid the tip-induced quantum dot. This enables unperturbed imaging of subtle density of states features in magnetic field such as the edge states in the quantum Hall regime. Moreover, we used the preparation technology to prepare high-level quantum dot arrays in semiconductor nanowires targeting its use for a novel type of scanning probe method with single-electron detection capability.

Link to the final report

https://oa.tib.eu/renate/handle/123456789/27135

Publications

• Ph.D. thesis, RWH Aachen: Interplay of quantum Hall edge states in graphene with the tip-induced quantum dot and graphene sample fabrication techniques for advanced scanning tunneling microscopy
  T. Johnsen
  
• Mapping quantum Hall edge states in graphene by scanning tunneling microscopy. Physical Review B, 107(11).
  Johnsen, T.; Schattauer, C.; Samaddar, S.; Weston, A.; Hamer, M. J.; Watanabe, K.; Taniguchi, T.; Gorbachev, R.; Libisch, F. & Morgenstern, M.
  
• Ph.D. thesis, RWTH Aachen: Development of a Charge Sensor in III- V Semiconductor Nanowires for Scanning Tunneling Microscopy
  F. Jekat